Manufacture of xylenes from reformate

ABSTRACT

A process is provided for the production of xylenes from reformate. The process is carried out by methylating the benzene, toluene, or both present in the reformate to produce a resulting product having a higher xylenes content than the reformate. Greater than equilibrium amounts of para-xylene can be produced by the process.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/465,119, filed Jun. 18, 2003, now abandoned which claims priority toU.S. Provisional Application No. 60/389,981, filed Jun. 19, 2002, whichis hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a process for producing xylenes from reformateby methylating benzene and/or toluene present in the reformate toproduce xylenes.

2. Description of the Prior Art

Most aromatics production is based on the recovery of aromatics derivedfrom catalytic reforming of naphtha. That process, using a feedcontaining a C₆+ hydrocarbons, typically produces a reformate comprisedof C₆-C₈ aromatics along with paraffins and heavier aromatics.

Aromatics can also be produced by the dehydrocyclo-oligomerization ofC₂-C₅ aliphatic hydrocarbons. That process typically produces a productcomprised of benzene, toluene, xylenes, C₅+ paraffins, C⁴⁻ lightparaffins, olefins, and unreacted C₂-C₅ aliphatic hydrocarbons.

Another technique for producing aromatics involves the cracking ofhydrocarbons such as by steam cracking or catalytic cracking. Thatprocess typically produces a product comprised of benzene, toluene,xylenes, C₆+ paraffins, and other hydrocarbons.

The aromatics present in the reformate stream from a reformer or crackerwill depend on the composition of the feedstock to the reformer orcracker, the type of reformer or cracker, and the operating conditionsof the reformer or cracker. Normally, the aromatics present in thereformate stream will comprise benzene, toluene, a near equilibriummixture of xylenes, ethylbenzene, and a mixture of nominally of C₉-C₁₀.Products of the reformate having the most value are benzene and xylenes.Of the xylene isomers, i.e., ortho-, meta- and para-xylene, thepara-xylene is of particular value as a large volume chemicalintermediate in a number of applications, such as the manufacture ofterephthalic acid, which is an intermediate in the manufacturer ofpolyester.

The reformate is usually sent to an aromatics recovery complex where itundergoes several processing steps in order to recover high valueproducts, e.g., xylenes and benzene, and to convert lower valueproducts, e.g., toluene, into higher value products. For example, thearomatics present in the reformate are usually separated into differentfractions by carbon number; e.g. benzene, toluene, xylenes, andethylbenzene, etc. The C₈ fraction is then subjected to a processingscheme to make more high value para-xylene. Para-xylene is usuallyrecovered in high purity from the C₈ fraction by separating thepara-xylene from the ortho-xylene, meta-xylene, and ethylbenzene usingselective adsorption or crystallization. The ortho-xylene andmeta-xylene remaining from the para-xylene separation are isomerized toproduce an equilibrium mixture of xylenes. The ethylbenzene isisomerized into xylenes or is dealkylated to benzene and ethane. Thepara-xylene is then separated from the ortho-xylene and the meta-xyleneusing adsorption or crystallization and the para-xylene-deleted-streamis recycled to extinction to the isomerization unit and then to thepara-xylene recovery unit until all of the ortho-xylene and meta-xyleneare converted to para-xylene and recovered.

Toluene is typically recovered as a separate fraction and then may beconverted into higher value products, e.g., benzene and/or xylenes. Onetoluene conversion process involves the disproportionation of toluene tomake benzene and xylenes. Another process involves the hydrodealkylationof toluene to make benzene.

Both toluene disproportionation and toluene hydrodealkylation result inthe formation of benzene. With the current and future anticipatedenvironmental regulations involving benzene, it is desirable that thetoluene conversion not result in the formation of significant quantitiesof benzene.

Xylenes can be produced by the methylation of toluene. Such a process isdisclosed in U.S. Pat. No. 3,965,207. One advantage of producing xylenesby this process is that the xylenes production does not result in theformation of benzene by-product.

In the past when it was desirable to methylate toluene, toluene presentin the reformate has usually been first separated from the otherhydrocarbons present in the reformate, such as by fractionation andextraction, before entering a methylation reactor. Such a separationrequires substantial capital investment in equipment, e.g., heatexchangers, high pressure separator, fractioners, etc. In addition, thereformate leaving the reformer is at elevated temperature and highlysuitable for further conversion. With the separation of toluene from thereformate, the recovered toluene must be heated again to conversiontemperatures.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a processfor producing xylenes from reformate, which process comprises:

(a) providing a reformate containing benzene, toluene or mixturesthereof in methylation reaction zone; and,

(b) methylating at least a portion of the benzene, toluene, or mixturesthereof present in said reformate in said methylation reaction zone witha methylating agent under conditions effective for the methylation andin the presence of a catalyst effective for the methylation to produce aresulting product having a higher xylenes content than said reformate.

In another embodiment, the present invention provides a process forproducing xylenes from reformate formed in an aromatization zone, whichprocess comprises:

(a) forming reformate containing benzene, toluene or mixtures thereof inan aromatization zone;

(b) transferring at least a portion of the reformate from saidaromatization zone to a methylation reaction zone; and,

(c) methylating at least a portion of the benzene, toluene, or mixturesthereof present in said reformate in said methylation reaction zone witha methylating agent under conditions effective for the methylation andin the presence of a catalyst effective for the methylation to produce aresulting product having a higher xylenes content than said reformate.

In a further embodiment, the present invention provides a multistageintegrated process for upgrading a petroleum naphtha which comprises thesteps of:

(a) introducing the naphtha to an aromatization zone;

(b) reforming the naphtha under aromatization conditions and in thepresence of a catalyst effective for the aromatization of the naphtha toproduce a reformate containing benzene, toluene or mixtures thereof;

(c) transferring at least a portion of said reformate from saidaromatization zone to a methylation reaction zone; and

(d) methylating in said methylation reaction zone at least a portion ofthe benzene, toluene or mixtures thereof present in said reformate witha methylating agent under conditions effective for the methylation andin the presence of a catalyst effective for the methylation to produce aresulting product having a higher xylenes content than said reformate.

An important feature of the present invention is that the aromatizationzone and methylation zone can be in series flow arrangement preferablywithout intermediate separation of the reformer effluent so that the twozones are operated under compatible conditions including hydrogencirculation rate and pressure.

The methylation reaction can occur in the liquid phase or the vaporphase. Usually the reaction will occur in the vapor phase. The presenceof the vapor phase in the reactor zone results in increased catalyticactivity in the reactor zone and increased diffusion of molecules to thecatalytic sites of the catalyst, e.g., pores of the molecular sieve. Theexpression “vapor phase”, as used herein, includes the presence of minoramounts of some liquid phase, e.g., less than 10 percent by volume ofliquid, as well as the substantial absence of liquid phase.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE is a simplified process flow diagram, illustrating apreferred embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The term “aromatization”, as used herein, shall mean the production ofaromatics comprising benzene, toluene, or mixtures thereof by theconversion of non-aromatic hydrocarbons to aromatic hydrocarbonscomprising benzene, toluene, or mixtures thereof. The term“aromatization”, as used herein, shall also include the production ofaromatics comprising benzene, toluene, or mixtures thereof by thecracking of heavy aromatic hydrocarbons to produce the aromatichydrocarbons comprising benzene, toluene, or mixtures. Examples ofaromatization processes include catalytic reforming of naphtha,dehydrocyclo-oligomerization of C₂-C₅ aliphatic hydrocarbons, steamcracking of hydrocarbons to produce aromatic hydrocarbons comprisingbenzene, toluene, or mixtures thereof, and the catalytic cracking ofhydrocarbons to produce aromatic hydrocarbons comprising benzene,toluene, or mixtures thereof.

The term “reformate”, as used herein, shall mean the product produced by“aromatization”.

In a preferred embodiment of the invention as depicted in the FIGURE, amethylation unit is located inside the reforming loop with reformatemethylation carried out without interstage separation.

Referring to the FIGURE, naphtha is directed via line 1 to heatexchanger 3 where the temperature of the naphtha is elevated. Thenaphtha feed can be either naphtha alone or the naphtha can be combinedwith toluene. Next, the heated naphtha is sent via line 5 to reformerheater 7 which elevates the temperature of the feed to a temperaturesuitable for reforming. After heating, the naphtha is withdrawn via line9 to aromatization reactor zone 11 where the naphtha is reformed intoaromatic products. Although only one reactor zone is shown, there can bemore than one reactor zone. The reformate is then withdrawn through line13 to heat exchanger 15 where the temperature of the reformate isadjusted for the methylation reaction. Next, the reformate is suppliedvia line 17 to methylation reaction zone 19. If desired, a stream ofhydrocarbons comprised of benzene and/or toluene can be added to thereformate. The methylation reaction is usually carried out in the vaporphase. When carried out in the vapor phase, if additional heat isnecessary for the reformate to be in the vapor phase, the reformate canbe heated to the vapor phase either before it enters the methylationreaction zone or after it has entered the methylation reaction zone. Themethylating agent can be supplied to methylation reaction zone 19 vialine 21. Usually the methylating agent is supplied to the methylationreaction zone through more than one feed point. In methylation reactionzone 19, the toluene present in the reformate is methylated to formxylenes. Also, benzene present in the reformate can be methylated toform toluene which, in turn, can be methylated to form xylenes.Depending upon the composition of the reformate, other reactions mayalso occur. For example, ethylbenzene can be methylated to formpara-ethyl-methylbenzene or dealkylated to form benzene, which in turn,can be methylated to form toluene which can be methylated to formxylenes. Also, any ethyl-methyl-benzene present in the reformate can bedealkylated to form toluene, which can be methylated to form xylenes.The catalyst used in the methylation reaction can be a catalyst thatproduces equilibrium amounts of xylene isomers or can be a catalyst thatis selective to produce greater than equilibrium amounts of a desiredxylene isomer, e.g., para-xylene. The methylated product is then sentvia line 23 to heat exchanger 3. Heat exchanger 3 cools the methylatedproduct and uses heat recovered from the methylated product to elevatethe temperature of the naphtha supplied via line 1. Next, the methylatedproduct is withdrawn through line 25 to heat exchanger 27 to furthercool the methylated product for separation of hydrogen from the product.Next, the cooled methylated product is sent via line 29 to high pressureseparator 31 where hydrogen is recovered. Hydrogen is removed via line33 and sent to water dryer/oxygenate removal unit 35. It is importantthat the water and oxygenates not be recycled with the hydrogen intoaromatization reaction zone 11. Hydrogen is removed from unit 35 vialine 36 and either recycled back to the reforming unit or removed fromthe system via line 37. Water present in the methylated product can beremoved from high pressure separator 31 via line 39. Next, the productis sent via line 41 to dryer 43 where remaining Water and oxygenates areremoved. The product is then sent via line 45 to separation block 47where low pressure hydrogen, C⁴⁻ and C₅ are separated and removed vialine 49. The resulting product, C₆+, is transferred via line 51 todistillation column 53 where C₆/C₇, including benzene and toluene, areremoved overhead via line 55 for further processing. The C₈+ fraction isremoved from the bottom of distillation column 53 via line 57 andfurther separated and converted in xylene loop 59 to the desiredmolecules, e.g., para-xylene and other by-products. Practicing of theinvention according to this embodiment allows sharing of the heatexchangers, furnace, compressor, phase separator, distillation, and theextraction hardware.

Aromatization

Aromatization will usually be carried out by catalytic reforming ofnaphtha or the dehydrocyclo-oligomerization of C₂-C₅ aliphatics.

Dehydrocyclo-oligomerization involves converting C₂-C₅ aliphatichydrocarbons to aromatic hydrocarbons. The process is carried out bycontacting C₂-C₅ aliphatic hydrocarbons in an aromatization zone and inthe presence of a catalyst suitable for dehydrocyclodimerization andunder conditions effective to produce a aromatics product comprisingbenzene and/or toluene. The dehydrocyclodimerization process increasescarbon chain length by oligomerization, promotes cyclization, anddehydrogenates cyclics to their respective aromatics.

The feedstream used in the dehydrocyclo-oligomerization process willcontain at least one aliphatic hydrocarbon containing 2 to about 5carbon atoms. The aliphatic hydrocarbons may be open chain, straightchain, or cyclic. Examples such as hydrocarbons include ethane,ethylene, propane, propylene, n-butane, n-butenes, isobutane, isobutene,butadiene, straight and branch pentane, pentene, and pentyldiene.Dehydrocyclo-oligomerization conditions will vary depending on suchfactors as feedstock composition and desired conversion. A desired rangeof conditions for the dehydrocyclodimerization of the aliphatichydrocarbons to aromatics include a temperature from about 350° to about650° C., a pressure from about 1 to about 100 atmospheres, and weighthour space velocity from about 0.2 to about 8. It is understood that, asthe average carbon number of the feed increases, a temperature in thelower end of temperature range is required for optimum performance andconversely, as the average carbon number of the feed decreases, thehigher the required reaction temperature.

The catalyst used in the dehydrocyclo-oligomerization reaction willpreferably comprise an intermediate pore size molecular sieve.Intermediate pore size molecular sieves have a pore size from about 5 toabout 7 Å and include, for example, AEL, AFI, MWW, MFI, MEL, MFS, MEI,MTW, EUO, MTT, HEU, FER, and TON structure type molecular sieves. Thesematerials are described in “Atlas of Zeolite Structure Types”, eds. W.H. Meier, D. H. Olson, and Ch. Baerlocher, Elsevier, Fourth Edition,1996, which is hereby incorporated by reference. Examples of suitableintermediate pore size molecular sieves include ZSM-5, ZSM-11, ZSM-12,ZSM-22, ZSM-23, ZSM-34, ZSM-35, ZSM-38, ZSM-48, ZSM-50, ZSM-57, MCM-22,MCM-49, MCM-56, and SAPO-5. Preferred molecular sieves are SAPO-11, aswell as titanosilicate, gallosilicate, aluminosilicate, andgallium-containing aluminosilicate molecular sieves having a MFIstructure.

Usually the molecular sieve will be combined with binder materialresistant to the temperature and other conditions employed in theprocess. Examples of suitable binder material include clays, alumina,silica, silica-alumina, silica-magnesia, silica-zirconia, silica-thoria,silica-beryllia, and silica-titania, as well as ternary compositions,such as silica-alumina-thoria, silica-alumina-zirconia,silica-alumina-magnesia and silica-magnesia-zirconia. The molecularsieve may also be composited with zeolitic material such as the zeoliticmaterials which are disclosed in U.S. Pat. No. 5,993,642, which ishereby incorporated by reference.

The relative proportions of molecular sieve and binder material willvary widely with the molecular sieve content ranging from between about1 to about 99 percent by weight, more preferably in the range of about10 to about 70 percent by weight of molecular sieve, and still morepreferably from about 20 to about 50 percent.

To make enhanced amounts (greater than equilibrium amounts) ofpara-xylene (versus the other xylene isomers produced by thedehydrocyclo-oligomerization reaction), a molecular sieve catalyst,e.g., ZSM-5 catalyst, can be selectivated by the use of a selectivatingagent.

Examples of compounds for selectivating the catalysts include treatingthe surface of the catalyst with compounds of phosphorus and/or variousmetal oxides such as alkaline earth metal oxides, e.g., calcium oxide,magnesium oxide, etc. rare earth metal oxides, lanthanum oxide, andother metal oxides such as boron oxide, titania, antimony oxide, andmanganese oxide.

Selectivation may also be accomplished by depositing coke on thecatalyst. The coke selectivation can be carried out during themethylation reaction such as by running the methylation reaction atconditions which allow the deposition of coke on the catalyst. Also, thecatalyst can be preselectivated with coke such as by exposing thecatalyst in the reactor to a thermally decomposable organic compound,e.g., benzene, toluene, etc. at a temperature in excess of thedecomposition temperature of said compound, e.g., from about 400° C. toabout 650° C., more preferably 425° C. to about 550° C., at a WHSV inthe range of from about 0.1 to about 20 lbs. of feed per pound ofcatalyst per hour, at a pressure in the range of from about 1 to about100 atmospheres, and in the presence of 0 to about 2 moles of hydrogen,more preferably from about 0.1 to about 1 moles of hydrogen per mole oforganic compound, and optionally in the presence of 0 to about 10 molesof nitrogen or another inert gas per mole of organic compound. Thisprocess is conducted for a period of time until a sufficient quantity ofcoke has deposited on the catalyst surface, generally at least about 2%by weight and more preferably from about 8 to about 40% by weight ofcoke.

Selectivation of the catalyst may also be accomplished usingorganosilicon compounds. The silicon compounds may comprise apolysiloxane include silicones, a siloxane, and a silane includingdisilanes and alkoxysilanes.

Silicone compounds that can be used in the present invention include thefollowing:

wherein R₁ is Hydrogen, Fluoride, Hydroxy, Alkyl, Aralkyl, Alkaryl orfluoro-alkyl. The hydrocarbon substituents generally contain from 1 toabout 10 carbon atoms and preferably are methyl or ethyl groups. R₂ isselected from the same group as R₁, and n is an integer of at least 2and generally in the range of 2 to about 1000. The molecular weight ofthe silicone compound employed is generally between about 80 to about20,000 and preferably about 150 to about 10,000. Representative siliconecompounds include dimethylsilicone, diethylsilicone,phenylmethylsilicone, methyl hydrogensilicone, ethylhydrogensilicone,phenylhydrogensilicone, fluoropropylsilicone,ethyltrifluoroprophysilicone, tetrachlorophenyl methylmethylethylsilicone, phenylethylsilicone, diphenylsilicone,methyltrisilicone, tetrachlorophenylethyl silicone, methylvinylsiliconeand ethylvinylsilicone. The silicone compound need not be linear but maybe cyclic as for example hexamethylcyclotrisiloxane,octamethylcyclotetrasiloxane, hexaphenyl cyclotrisiloxane andoctaphenylcyclotetrasiloxane. Mixtures of these compounds may also beused as well as silicones with other functional groups.

Useful siloxanes and polysiloxanes include as non-limiting examplehexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, hexamethyldisiloxane, octamethytrisiloxane,decamethyltetrasiloxane, hexaethylcyclotrisiloxane, octaethylcyclotetrasiloxane, hexaphenylcyclotrisiloxane andoctaphenylcyclo-tetrasiloxane.

Useful silanes, disilanes, or alkoxysilanes include organic substitutedsilanes having the general formula:

wherein R is a reactive group such as hydrogen, alkoxy, halogen,carboxy, amino, acetamide, trialkylsilyoxy, R₁, R₂ and R₃ can be thesame as R or can be an organic radical which may include alkyl of from 1to about 40 carbon atoms, alkyl or aryl carboxylic acid wherein theorganic portion of alkyl contains 1 to about 30 carbon atoms and thearyl group contains about 6 to about 24 carbons which may be furthersubstituted, alkylaryl and arylalkyl groups containing about 7 to about30 carbon atoms. Preferably, the alkyl group for an alkyl silane isbetween about 1 and about 4 carbon atoms in chain length. Mixtures mayalso be used.

The silanes or disilanes include, as non-limiting examples,dimethylphenylsilane, phenylrimethylsilane, triethylsilane andhexamethyldislane. Useful alkoxysilanes are those with at least onesilicon-hydrogen bond.

Selectivation of the catalyst can also be accomplished using acombination of coke and silicon applied by the procedures describedabove.

Catalytic reforming involves the production of aromatics from a C₆+paraffinic feed, e.g., naphtha, by contacting the feed with a reformingcatalyst under reforming conditions to produce a reaction productcomprising aromatics and paraffins. The reformate is formed undertypical reforming conditions designed to promote dehydrogenation ofnaphthenes, isomerization of paraffinic hydrocarbons anddehydrocyclization of non-aromatic hydrocarbons.

Catalysts suitable for use in catalytic reforming include acidicreforming catalysts (bifunctional catalysts) and non-acidic reformingcatalysts (monofunctional catalysts).

Acidic reforming catalysts usually comprise a metallic oxide supporthaving disposed therein a Group VIII metal. Suitable metallic oxidesupports include alumina and silica. Preferably, the acidic reformingcatalyst comprises a metallic oxide support having disposed therein inintimate admixture a Group VIII metal (preferably platinum) and a metalpromoter, such as rhenium, tin, germanium, cobalt, nickel, iridium,rhodium, ruthenium and combinations thereof. More preferably, the acidicreforming catalyst comprises an alumina support, platinum, and rheniumor platinum and tin on an alumina support.

Non-acidic or monofunctional reforming catalysts will comprise anon-acidic molecular sieve, e.g., zeolite, and one or morehydrogenation/dehydrogenation components. Examples of suitable molecularsieves include MFI structure type, e.g., silicalite, and molecularsieves having a large pore size, e.g., pore size from about 7 to 9Angstroms. Examples of large pore molecular sieves include LTL, FAU, and*BEA structure types. Examples of specific molecular sieves includezeolite L, zeolite X, zeolite Beta, zeolite Y, and ETS-10.

The non-acidic catalysts will contain one or morehydrogenation/dehydrogenation metals, e.g., Group VII B metals, such asrhenium, and Group VIII metals, such as nickel, ruthenium, rhodium,palladium, iridium or platinum. The preferred Group VIII metal isplatinum. Also, the nonacidic catalyst can contain a metal promoter suchas tin.

The amount of hydrogenation/dehydrogenation metal present on thenon-acidic catalyst will usually be from about 0.1% to about 5% ofhydrogenation/dehydrogenation metal based on the weight of the catalyst.The metal can incorporated into the zeolite during synthesis of thezeolite, by impregnation, or by ion exchange of an aqueous solutioncontaining the appropriate salt. By way of example, in an ion exchangeprocess, platinum can be introduced by using cationic platinum complexessuch as tetraammine-platinum (II) nitrate.

The non-acidic catalyst will usually include a binder. The binder can bea natural or a synthetically produced inorganic oxide or combination ofinorganic oxides. Typical inorganic oxide supports which can be usedinclude clays, alumina, and silica, in which acidic sites are preferablyexchanged by cations that do not impart strong acidity.

The reforming process can be continuous, cyclic or semi-regenerative.The process can be in a fixed bed, moving bed, tubular, radial flow orfluid bed.

Conditions for reforming conditions include temperatures of at leastabout 400° C. to about 600° C. and pressures from about 50 psig (446kPa) to about 500 psig (3,549 kPa), a mole ratio of hydrogen tohydrocarbons from 1:1 to 10:1 and a liquid hour space velocity ofbetween 0.3 and 10.

Substantially any hydrocarbon feed containing C₆+ e.g., naphtha can beutilized. The naphtha will generally comprise C₆-C₉ aliphatichydrocarbons. The aliphatic hydrocarbons may be straight or branchedchain acyclic hydrocarbons, and particularly paraffins such as heptane.

Toluene/Benzene Methylation

The methylation reaction will usually occur in vapor phase. Reactionconditions for use in the present invention include temperatures fromabout 300° C. to about 700° C. and preferably about 400° C. to about700° C. The reaction is preferably carried out at a pressure from about1 to 1000 psig, and a weight hourly space velocity of between about 0.1and about 200 and preferably between about 1 and about 100 weight ofcharge per weight of catalyst per hour. The molar ratio of toluene andbenzene to methylating agent can vary and will usually be from about0.1:1 to about 20:1. Preferred ratios for operation are in the range of2:1 to about 4:1. Hydrogen gas can be supplied to the reaction as ananticoking agent and diluent. The methylating agent is usually suppliedto the methylation reaction zone through multiple feed points, e.g., 3-6feed points.

Typical methylating agents include methanol, dimethylether,methylchloride, methylbromide, methylcarbonate, acetaldehyde,dimethoxyethane, acetone, and dimethylsulfide. The methylating agent canalso be formed from synthesis gas, e.g., the agent can be formed fromthe H₂, CO, and/or CO₂ of synthesis gas. The methylating agent can beformed from the synthesis gas within the methylation reaction zone. Oneskilled in the art will know that other methylating agents may beemployed to methylate the benzene and/or toluene based on thedescription provided therein. Preferred methylating agents are methanoland dimethylether. Methanol is most preferred.

Catalysts suitable for use in the present invention include any catalystthat is effective for toluene or benzene methylation. The catalyst usedin the process will usually comprise a crystalline molecular sieve.

The catalyst used in the methylation reaction will preferably comprisean intermediate pore size molecular sieve. Intermediate pore sizemolecular sieves have a pore size from about 5 to about 7. A andinclude, for example, AEL, AFI, MWW, MFI, MEL, MFS, MEI, MTW, EUO, MTT,HEU, FER, and TON structure type zeolites. These materials are describedin “Atlas of Zeolite Structure Types”, eds. W. H. Meier, D. H. Olson,and Ch. Baerlocher, Elsevier, Fourth Edition, 1996, which is herebyincorporated by reference. Examples of suitable intermediate pore sizemolecular sieves include ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-34,ZSM-35, ZSM-38, ZSM-48, ZSM-50, ZSM-57, MCM-22, MCM-49, MCM-56, andSAPO-5. Preferred molecular sieves are SAPO-11, as well astitanosilicate, gallosilicate, aluminosilicate, and gallium-containingaluminosilicate molecular sieves having a MFI structure.

The intermediate pore size molecular sieve will generally be acomposition having the following molar relationship:X₂O₃:(n)YO₂wherein X is a trivalent element such as titanium, aluminum, iron,boron, and/or gallium and Y is a tetravalent element such as silicon,tin, and/or germanium; and n has a value greater than 12, said valuebeing dependent upon the particular type of molecular sieve. When theintermediate pore size molecular sieve is a MFI structure type molecularsieve, n is preferably greater than 10 and preferably, from 20:1 to200:1.

When the molecular sieve has a gallium silicate composition, themolecular sieve usually will be a composition having the following molarrelationship:Ga₂O₃:ySiO₂wherein y is between about 20 and about 500. The molecular sieveframework may contain only gallium and silicon atoms or may also containa combination of gallium, aluminum, and silicon.

Usually the molecular sieve will be incorporated with binder materialresistant to the temperature and other conditions employed in theprocess. Examples of suitable binder material include clays, alumina,silica, silica-alumina, silica-magnesia, silica-zirconia, silica-thoria,silica-beryllia, and silica-titania, as well as ternary compositions,such as silica-alumina-thoria, silica-alumina-zirconia,silica-alumina-magnesia and silica-magnesia-zirconia. The molecularsieve may also be composited with zeolitic material such as the zeoliticmaterials which are disclosed in U.S. Pat. No. 5,993,642.

The relative proportions of molecular sieve and binder material willvary widely with the molecular sieve content ranging from between about1 to about 99 percent by weight, more preferably in the range of about10 to about 70 percent by weight of molecular sieve, and still morepreferably from about 20 to about 50 percent.

The catalyst may also include at least one hydrogenation/dehydrogenationmetal. Such metals can reduce the rate of deactivation of the catalyst.Reference to hydrogenation/dehydrogenation metal or metals is intendedto encompass such metal or metals in the elemental state (i.e. zerovalent) or in some other catalytically active form such as an oxide,sulfide, halide, carboxylate and the like. Such metals are known topersons skilled in the art and include, for example, one or more metals,and metals of Groups IIIA, IVA, VA, VIA, VIIA, VIII, IB, IIB, IIIB, IVB,VB, VIB, and VIIB of the Periodic Table of the Elements. Examples ofsuitable metals include Group VIII metals (i.e., Pt. Pd, Ir, Rh, Os, Ru,Ni, Co and Fe), Group IVA metals (i.e., Sn and Pb), Group VA metals(i.e., Sb and Bi), and Group VIIB metals (i.e., Mn, Tc and Re). Noblemetals (i.e., Pt, Pd, Ir, Rh, Os and Ru) are sometimes preferred.

When the catalyst used for the methylation reaction is a molecularsieve, the catalyst can be selectivated to enhance the amount ofpara-xylene produced by the methylation reaction by the use of aselectivating agent. Suitable selectivating agents include theselectivating agents disclosed earlier in this application forselectivating dehydrocyclo-oligomerization molecular sieve catalysts.

Catalysts particularly suited for the methylation reaction are zeolitebound zeolite catalysts. These catalysts, as well as their method ofpreparation, are described in U.S. Pat. No. 5,994,603, which is herebyincorporated by reference. The zeolite bound zeolite catalysts willcomprise first crystals of an acidic intermediate pore size firstmolecular sieve and a binder comprising second crystals of a secondmolecular sieve. Preferably, the zeolite bound zeolite catalyst containsless than 10 percent by weight based on the total weight of the firstand second zeolite of non-zeolitic binder, e.g., amorphous binder. Anexample of such a catalyst comprises first crystals of a MFI or MELstructure type, e.g., ZSM-5 or ZSM-11, and a binder comprising secondcrystals of MFI or MEL structure type, e.g., Silicalite 1 or Silicalite2.

The amount of benzene/toluene converted to xylenes will depend on anumber of factors including the make up of the reformate to bemethylated, the methylation conditions, and the catalyst used. Usually,at least 5 weight percent of the benzene/toluene will be converted toxylenes. Preferably, at least 7 weight percent of the benzene/toluenewill be converted to xylenes, and, more preferably, at least 30 weightpercent of the benzene/toluene will be converted to xylenes.

The process of methylation of the benzene, toluene, or mixtures thereofpresent in the reformate can produce greater than equilibrium amounts ofpara-xylene. Preferably, the process will produce a xylene productcontaining greater than 30 weight percent para-xylene based on the totalweight of xylenes produced by the process. More preferably, the processproduces a xylene product containing greater than 60 weight percentpara-xylene based on the total weight of the xylenes produced by theprocess. Most preferably, the process produces a xylene productcontaining greater than 80 weight percent para-xylene based on the totalweight of the xylenes produced by the process.

The invention is further exemplified by the examples below, which arepresent to illustrate certain specific embodiments of the invention, butare not intended to be construed as to be restrictive of the spirit andscope thereof.

Example 1

A simulated light naphtha reformate feed was subjected to toluenemethylation. The catalyst used in the test comprised 1/16 inchextrudates which contained 65 weight percent H-ZSM-5 and 35 weightpercent silica binder. The catalyst had an alpha value of 330. The“alpha value” of a catalyst is an approximate indication of itscatalytic cracking activity. The alpha test is described in U.S. Pat.No. 3,354,078 and in the Journal of Catalysis, Vol. 4, 522-529 (1965);Vol. 6, 278 (1966); and Vol. 61, 395 (1980), each incorporated herein byreference to that description.

The reformate feed used in the test had the composition given below:

TABLE 1 Component Wt. % C⁵⁻ 0.00 n-C₆ 18.58 i-C₆ 15.04 n-C₇ 4.30 i-C₇5.37 Benzene 15.32 Toluene 41.38 PX 0.00 MX 0.00 OX 0.00 EB 0.00 C₉₊0.00 Total 100

The test was carried out under the following conditions:

TABLE 2 Component WHSV ((h⁻¹) 1 MeOH/:Toluene [molar] 1 H2:(MeOH + HCs)[molar] 1 Pressure (psig) 64 Temperature (° F.) 700

The test was carried out by loading the catalyst into a fixed bedreactor and heating the catalyst in flowing hydrogen at reactortemperature range from room temperature to 950° F. for two hours. Next,the reformate was introduced into the reactor and the test was carriedout under the conditions shown in Table 2. The results of the test areset forth below in Table 3.

TABLE 3 Component Wt. % C⁵⁻ 1.13 n-C₆ 16.58 i-C₆ 13.43 n-C₇ 3.87 i-C₇4.33 Benzene 11.06 Toluene 35.82 PX 2.59 MX 3.20 OX 3.76 EB 0.00 C₉₊4.23 Total 100

The results report in Table 3 shows that after toluene methylation, thecontent of the reformate increased from no xylenes being present to9.49% xylenes. Also, the amount of para-xylene produced (27%para-xylene) was greater than an equilibrium amount (24% para-xylene).

Example 2

A simulated light naphtha reformate feed was subjected to toluenemethylation using a silicon-selectivated H-ZSM-5/silica bound catalyst.

The catalyst was selectivated by contacting H-ZSM-5/silica bound (65weight % H-ZSM-5 35 weight % silica) with dimethylphenylmethylpolysiloxane dissolved in decane and subsequently calcining theselectivated catalyst. The catalyst was treated with 3 additionalsilicon selectivation treatments using substantially the same procedure.The catalyst had an alpha value of approximately 300.

The reformate feed used in the test had the composition given below:

TABLE 4 Component Wt. % C⁵⁻ 0.00 n-C₆ 27.85 i-C₆ 3.64 n-C₇ 8.77 i-C₇0.05 Benzene 15.76 Toluene 43.93 PX 0.00 MX 0.00 OX 0.00 EB 0.00 C₉₊0.00 Total 100

The test was carried out under the following conditions:

TABLE 5 Component WHSV (h⁻¹) 1 MeOH/:Toluene [molar] 1 H2:(MeOH + HCs)[molar] 1 Pressure (psig) 200 Temperature (° F.) 700

The test was carried out by loading the catalyst into a fixed bedreactor and heating the catalyst in flowing hydrogen at a reactortemperature range from room temperature to 950° F. for two hours. Next,the reformate was introduced into the reactor and the test was run atthe conditions shown in Table 5. The results of the test are set forthbelow in Table 6.

TABLE 6 Component Wt. % C⁵⁻ 5.61 n-C₆ 21.32 i-C₆ 3.85 n-C₇ 5.44 i-C₇0.22 Benzene 11.39 Toluene 33.12 PX 2.66 MX 3.67 OX 2.36 EB 1.31 C₉₊9.05 Total 100

The results in Table 6 shows that after toluene methylation, the contentof the reformate increased from no xylenes being present to 8.69%xylenes. Also, the amount of para-xylene produced (31% para-xylene) wasgreater than an equilibrium amount (24% para-xylene).

Example 3

A simulated light naphtha reformate feed was subjected to toluenemethylation using a zeolite bound zeolite catalyst.

The catalyst comprised 70 wt. % H-ZSM-5 core crystals (average particlesize of 3.5 microns) having a silica to alumina mole ratio of 75:1 and30 wt. % ZSM-5 binder crystals having a silica to mole ratio ofapproximately 900:1. The catalyst was prepared by first mixing the ZSM-5core crystals with amorphous silica containing a trace amount of aluminaand then extruding the mixture into a silica bound extrudate. Next, thesilica binder of the extrudate was converted to the second zeolite byaging the aggregate at elevated temperatures in an aqueous solutioncontaining a template and hydroxy ions sufficient to covert the silicato the binder crystals. The resulting zeolite bound zeolite was thenwashed, dried, calcined, and ion exchanged into the hydrogen form.

The reformate feed used in the test had the composition given below:

TABLE 7 Component Wt. % C⁵⁻ 0.00 n-C₆ 33.45 i-C₆ 3.88 n-C₇ 0.00 i-C₇0.00 Benzene 16.01 Toluene 46.66 PX 0.00 MX 0.00 OX 0.00 EB 0.00 C₉₊0.00 Total 100

The test was carried out under the following conditions:

TABLE 8 Component WHSV (h⁻¹) 4 MeOH/:Toluene [molar] 1 H2:(MeOH + HCs)[molar] 1 Pressure (psig) 200 Temperature (° F.) 700

The test was carried out by loading the catalyst into a fixed bedreactor and heating the catalyst in flowing hydrogen at reactortemperature range from room temperature to 950° F. for two hours. Next,the reformate was introduced into the reactor and the test was carriedout at the conditions shown in Table 8. The results of the test are setforth below in Table 9.

TABLE 9 Component Wt. % C⁵⁻ 4.42 n-C₆ 26.69 i-C₆ 3.77 n-C₇ 0.00 i-C₇0.00 Benzene 13.21 Toluene 39.40 PX 2.18 MX 2.41 OX 1.79 EB 0.90 C₉₊5.24 Total 100

The results in Table 6 shows that after toluene methylation, the contentof the reformate increased from no xylenes being present to 6.38%xylenes. Also, the amount of para-xylene produced (34% para-xylene) wasgreater than an equilibrium amount (24% para-xylene).

Example 4

A simulated light reformate, which would be formed by thedehydrocyclo-oligomerization of C₂-C₅ aliphatic hydrocarbons, wassubjected to toluene methylation. The catalyst used in the test had analpha value of approximately 22 and comprised 1/16 inch extrudates whichcontained 65 wt. % H-ZSM-23 having a silica to alumina mole ratio of110:1 and 35 wt. % of alumina binder. The ZSM-23 was prepared accordingto U.S. Pat. No. 4,076,842.

The reformate feed used in the test had the composition given below:

TABLE 10 Component Wt. % C⁵⁻ 0.00 n-C₆ 0.00 i-C₆ 0.00 n-C₇ 35.00 i-C₇5.00 Benzene 15.00 Toluene 45.00 PX 0.00 MX 0.00 OX 0.00 EB 0.00 C₉₊0.00 Total 100

The test was carried out under the following conditions:

TABLE 11 Component WHSV (h⁻¹) 8 MeOH/:Toluene [molar] 1/3 H2:(MeOH +HCs) [molar] 2 Pressure (psig) 150 Temperature (° F.) 932

The test was carried out by loading the catalyst into a fixed bedreactor and heating the catalyst in flowing hydrogen to the reactiontemperature. Next, the reformate was introduced into the reactor and thetest was run at the conditions shown in Table 11. The results of thetest are set forth below in Table 12.

TABLE 12 Component Wt. % C⁵⁻ 19.25 n-C₆ 0.00 i-C₆ 0.00 n-C₇ 16.10 i-C₇4.65 Benzene 13.07 Toluene 41.45 PX 2.74 MX 1.83 OX 0.91 EB 0.00 C₉₊0.00 Total 100

The results in Table 12 show that after toluene methylation, the contentof the reformate increased from no xylenes being present to 5.48%xylenes. Also, the amount of para-xylene produced (50% para-xylene) wasgreater than an equilibrium amount (24% para-xylene).

Example 5

A simulated full range naphtha reformate (without C₁-C₅ hydrocarbons)was subjected to toluene methylation using a silica selectivated ZSM-5catalyst.

The ZSM-5 catalyst was selectivated using the procedure described abovein Example 2. The catalyst had an alpha value of approximately 300.

The reformate feed used in the test had the composition given below:

TABLE 13 Component Wt. % C⁵⁻ 0.00 n-C₆ 33.12 i-C₆ 3.69 n-C₇ 0.00 i-C₇0.00 Benzene 15.85 Toluene 47.35 PX 0.00 MX 0.00 OX 0.00 EB 0.00 C₉₊0.00 Total 100

The test was carried out under the following conditions:

TABLE 14 Component WHSV (h⁻¹) 9.2 MeOH/:Toluene [molar] 0.37 H2:(MeOH +HCs) [molar] 2 Pressure (psig) 200 Temperature (° F.) 700

The test was carried out by loading the catalyst into a fixed bedreactor and heating the catalyst in flowing hydrogen at a reactortemperature range from room temperature to 950° F. for two hours. Next,the reformate was introduced into the reactor and the test was run atthe conditions shown in Table 14. The product contained greater than 90%para-xylene based on the total amount of xylenes in the product.

Example 6

A simulated light reformate, which would be formed by thedehydrocyclo-oligomerization of C₂-C₅ aliphatic hydrocarbons, wassubjected to toluene methylation using a SAPO-11 catalyst. The catalysthad an alpha value of approximately 52 and its chemical analysis wasSi_(0.1)Al_(0.46)P_(0.44). The SAPO-11 was prepared according to U.S.Pat. No. 6,294,493

The reformate feed used in the test had the composition given below:

TABLE 15 Component Wt. % C⁵⁻ 0.00 n-C₆ 0.00 i-C₆ 0.00 n-C₇ 35.00 i-C₇5.00 Benzene 15.00 Toluene 45.00 PX 0.00 MX 0.00 OX 0.00 EB 0.00 C₉₊0.00 Total 100

The test was carried out under the following conditions:

TABLE 16 Component WHSV (h⁻¹) 8 MeOH/:Toluene [molar] 1/3 H2:(MeOH +HCs) [molar] 2 Pressure (psig) 150 Temperature (° F.) 932

The test was carried out by loading the catalyst into a fixed bedreactor and heating the catalyst in flowing hydrogen to the reactiontemperature. Next, the reformate was introduced into the reactor and thetest was run at the conditions shown in Table 16. The results of thetest are set forth below in Table 17.

TABLE 17 Component Wt. % C⁵⁻ 19.25 n-C₆ 0.00 i-C₆ 0.00 n-C₇ 16.10 i-C₇4.65 Benzene 13.07 Toluene 41.45 PX 2.74 MX 1.83 OX 0.91 EB 0.00 C₉₊0.00 Total 100

The results in Table 17 shows that after toluene methylation, thecontent of the reformate increased from no xylenes being present to 5.8%xylenes. Also, the amount of para-xylene produced was greater than 40%para-xylene.

1. A process for producing xylenes from reformate formed in an aromatization zone, which process consists of: (a) forming reformate in an aromatization zone comprising a reforming loop, said reformate comprising aromatic compounds selected from the group consisting of benzene, toluene and mixtures thereof then (b) transferring reformate from said aromatization zone to a methylation reaction zone, wherein said methylation reaction zone is located inside said reforming loop; and, then (c) methylating at least a portion of the benzene, toluene, or mixtures thereof present in said reformate in said methylation reaction zone with a methylating agent under vapor phase conditions effective for the methylation and in the presence of a catalyst selected from at least one of the group consisting of ZSM-5, ZSM-23, and SAPO-11 to produce a resulting product having a higher xylenes content than said reformate.
 2. The process of claim 1, wherein step (a) consists of the catalytic reforming of naphtha.
 3. The process of claim 1, wherein the catalyst in step (c) is ZSM-5.
 4. The process of claim 1, wherein the catalyst in step (c) is ZSM-23.
 5. The process of claim 1, wherein the catalyst in step (c) is SAPO-11.
 6. The process of claim 1, wherein step (a) consists of the dehydrocyclo-oligomerization of C₂-C₅ aliphatics. 